In the munitions arts, a cartridge includes a case, a bullet, propellant, and a primer. Such cartridges are used in firearms and the operation of such cartridges is generally well known in the art. To discharge a cartridge in a firearm, a user typically squeezes a trigger to activate a firing pin and the firing pin strikes the primer, causing the propellant to ignite. The ignited propellant creates substantial pressure within the cartridge, and the bullet is forcefully ejected from the cartridge and from the firearm.
A cartridge case generally extends between two ends, a base end and a forward end. The base end is generally closed and includes features for receiving the primer. The forward end is generally open, with the bullet being inserted into this forward open end of the cartridge case. A volume is defined within the cartridge case between the base end and the forward end, and the propellant is contained within that volume. Modern cartridges use so-called “smokeless powder” as the propellant, and for the purposes of this disclosure, the volume where the propellant is contained will be called the powder fill pocket. The cartridge case also includes a generally tubular outer wall having a generally constant diameter, and a web that extends transverse to the outer wall proximate the base end. A primer pocket is formed between the web and the base end and a flash hole connects the primer pocket with the powder fill pocket.
The exterior of a cartridge case can take on any suitable shape. Known cartridge cases have bases with several different profiles. Proximate the base end, cartridge cases are generally cylindrical in shape. When viewed in the cross section taken along the diameter and showing the length axis of a cartridge case, the outer wall has a generally constant diameter, except for near the base end. Proximate the base end structures such as rims, extraction grooves and belts may be found. In one known example, the diameter of the cartridge case is smaller than a rim positioned at the base end of the cartridge case. Such a design is referred to in the art as a rimmed cartridge case. In another known cartridge case design, the outer wall of the cartridge case tapers radially inwardly to form an extraction groove proximate the base end, and the extraction groove includes a lip that does not extend beyond the diameter of the outer wall. Such design is known in the art as a rimless cartridge case because the lip of the extraction groove does not extend beyond the outer wall. Such is different from the rim of the rimmed design, which extends beyond the diameter of the outer wall. In yet another cartridge case design, the outer wall of the cartridge case tapers near the base end to define an extraction groove and a lip extends slightly beyond the diameter of the outer wall. Such a design is known as a semi-rimmed cartridge case. In another known cartridge case design, a belt extends radially outwardly from the outer wall proximate the base end, then tapers radially inwardly to define an extraction groove and a lip, much like the extraction groove and lip found in rimless designs. Such a design is known as a belted cartridge case. In yet another cartridge case design, the outer wall tapers radially inwardly near the base end to define a groove, and the groove has a lip that does not extend as far as the diameter of the outer wall. Such a design is known as rebated cartridge case.